"When you pay for any app, you don't want someone tracking you, looking at my browsing habits, or collecting personal data about you," he said. "Apparently that doesn't stop when you pay for an app. The app only stops displaying pop-ups and banners."

Subtly siphoning data

According to Bitdefender's analysis of the top paid apps in Google Play with both paid and free versions, five of eight paid apps siphoned information from a mobile device as aggressively as their free counterparts.

"Indeed, the main difference between paid and free versions—at least in terms of privacy—is that the intrusiveness is simply hidden better in paid apps," Bitdefender reports.

Among the paid apps that continued tracking and uploading user location, as well as broadcasting unique device IDs to third-party servers, even after purchase, were Rovio's Angry Birds Space, Angry Birds Star Wars, SwiftKey Keyboard, SoundHound, and Cut the Rope.

Apps less attractive?

"The use of aggressive tracking in paid apps, if it becomes widely known, could devalue paid versions and change consumer behavior," Bitdefender predicted.

That's not something that developers of paid Android apps want to hear, since they already have a problem selling shoppers for Android apps on paying for them. For example, app market watcher Distimo noted on a typical day in November 2012, Google Play raked in $3.5 million from apps, compared to $15 million garnered by Apple's app store.

Bitdefender's latest findings may just be the tip of the ice berg at Google Play, according to Arsene. "If this is what the top ten apps are doing, you can imagine what apps that are not that popular are doing," he said.